linux-kernel - Re: [PATCH 11/27] mm: refactor the ZONE_DEVICE handling in migrate_vma_insert

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Date:   Thu, 10 Feb 2022 21:48:32 +1100
From:   Alistair Popple <apopple@...dia.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Christoph Hellwig <hch@....de>
CC:     Felix Kuehling <Felix.Kuehling@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        Ben Skeggs <bskeggs@...hat.com>,
        Karol Herbst <kherbst@...hat.com>,
        Lyude Paul <lyude@...hat.com>, Jason Gunthorpe <jgg@...pe.ca>,
        Logan Gunthorpe <logang@...tatee.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        <linux-kernel@...r.kernel.org>, <amd-gfx@...ts.freedesktop.org>,
        <dri-devel@...ts.freedesktop.org>, <nouveau@...ts.freedesktop.org>,
        <nvdimm@...ts.linux.dev>, <linux-mm@...ck.org>
Subject: Re: [PATCH 11/27] mm: refactor the ZONE_DEVICE handling in migrate_vma_insert_page

Reviewed-by: Alistair Popple <apopple@...dia.com>

On Thursday, 10 February 2022 6:28:12 PM AEDT Christoph Hellwig wrote:
> Make the flow a little more clear and prepare for adding a new
> ZONE_DEVICE memory type.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  mm/migrate.c | 31 +++++++++++++++----------------
>  1 file changed, 15 insertions(+), 16 deletions(-)
> 
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 8e0370a73f8a43..30ecd7223656c1 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -2670,26 +2670,25 @@ static void migrate_vma_insert_page(struct migrate_vma *migrate,
>  	 */
>  	__SetPageUptodate(page);
>  
> -	if (is_zone_device_page(page)) {
> -		if (is_device_private_page(page)) {
> -			swp_entry_t swp_entry;
> +	if (is_device_private_page(page)) {
> +		swp_entry_t swp_entry;
>  
> -			if (vma->vm_flags & VM_WRITE)
> -				swp_entry = make_writable_device_private_entry(
> -							page_to_pfn(page));
> -			else
> -				swp_entry = make_readable_device_private_entry(
> -							page_to_pfn(page));
> -			entry = swp_entry_to_pte(swp_entry);
> -		} else {
> -			/*
> -			 * For now we only support migrating to un-addressable
> -			 * device memory.
> -			 */
> +		if (vma->vm_flags & VM_WRITE)
> +			swp_entry = make_writable_device_private_entry(
> +						page_to_pfn(page));
> +		else
> +			swp_entry = make_readable_device_private_entry(
> +						page_to_pfn(page));
> +		entry = swp_entry_to_pte(swp_entry);
> +	} else {
> +		/*
> +		 * For now we only support migrating to un-addressable device
> +		 * memory.
> +		 */
> +		if (is_zone_device_page(page)) {
>  			pr_warn_once("Unsupported ZONE_DEVICE page type.\n");
>  			goto abort;
>  		}
> -	} else {
>  		entry = mk_pte(page, vma->vm_page_prot);
>  		if (vma->vm_flags & VM_WRITE)
>  			entry = pte_mkwrite(pte_mkdirty(entry));
>